1. Field of the Invention
This invention relates to a new formaldehyde-free process for imparting wrinkle resistance and smooth drying properties to textiles.
2. Description of the Prior Art
Many types of cellulose crosslinking agents have previously been proposed as durable press finishing reagents to render cotton textiles wrinkle resistant in the dry state at ordinary humidity, and to make such textiles smooth drying when laundered in the wet state and then dried. In actual practice however, commercial high-speed durable press finishing of fabric is carried out exclusively with formaldehyde derivatives of cyclic and acyclic ureas or amides, and those derivatives are commonly referred to as N-methylol agents or N-methylolamides. They have the advantage of a high rate of reaction with cotton cellulose, they have been shown to cause less strength loss in the fabric than does formaldehyde or other non-nitrogenous agents, as conventionally applied, and they are readily available at low cost.
However, without exception, the N-methylol agents have the disadvantage of releasing vapors of free formaldehyde continuously during the durable press treatment of fabric, subsequent storage of finished fabric, garment manufacture from finished fabric, finished garment storage in retail outlets, and finally in the use of finished textile or apparel goods by the consumer. The widely observed irritating effect of formaldehyde vapor released by the treated fabric, effects on the eyes and skin of persons handling or wearing durable press textiles and garments, and the knowledge that formaldehyde is a carcinogen in test animals and may be a carcinogen in humans, has created a need for durable press finishing agents that are not based on formaldehyde or its derivatives.
It is known from the work of Gonzales et al, American Dyestuff Reporter 58 [3 ] 27-29 (1969) that glyoxal, also known as ethanedial, the structure of which in monomeric anhydrous form is O.dbd.CH--CH.dbd.O, shows marked reactivity toward cotton cellulose when applied in the presence of magnesium chloride and crosslinks the cellulose to impart a moderate level of wrinkle resistance to cotton fabric. Although the fabric weight gains obtained with glyoxal alone correspond to a low reaction efficiency, the presence of glycolic acid increased the rate of reaction and the final wrinkle recovery considerably. However, the strength losses also increased, being 70% for breaking strength and 75% for tearing strength. The use of aluminum nitrate, sulfate and chloride catalysts with mixtures of glyoxal and dimethylol urea to crosslink hydroxyethylcellulose was described by Pastyr et al, Czechoslovakian Pat. No. 172, 160 (Chemical Abstracts 89 131030v (1978)).
Worth (U.S. Pat. No. 4,269,603) has shown that a combination of aluminum sulfate and magnesium sulfate catalyze the crosslinking of cotton by glyoxal in the presence of a "reactive silicone" as fabric softener. Extremely high curing temperatures of 350.degree.-400.degree. F., corresponding to 177.degree.-204.degree. C., were preferred. It is known that cotton yarn and fabric lose strength fairly rapidly at these temperatures in air. The strength properties of treated fabrics were satisfactory in the case of blend fabrics containing 65% polyester-35% cotton, where most of the strength was provided by the polyester fibers, but the strength retentions were not disclosed in the case of fabrics containing as much as 50%-100% cotton. High levels of wrinkle resistance and smooth drying performance were imparted at all levels of cotton content in the fabrics. It was subsequently shown by Welch et al, Textile Research Journal 52 149-157 (1982) that aluminum sulfate was a highly effective catalyst for glyoxal crosslinking of cotton at 140.degree.-155.degree. C., but even at these more moderate cure temperatures, extremely high strength losses occurred when treating 100% cotton fabric. Even with a fabric softener present, tearing strength losses were 71%-74% and breaking strength losses were 72%-73% when applying a moderate concentration of glyoxal. Yellowing occurred in heat curing the fabric, unless ethylene glycol or glycerol were present as coreactant additives in the glyoxal-aluminum sulfate formulation which was applied to the fabric. The additives noticeably increased the durable press appearance ratings, but slightly decreased the wrinkle recovery angles. Attempts to use metal halides as catalysts were unsuccessful because of the fabric discoloration they produced under the conditions required to impart useful levels of wrinkle resistance and smooth drying performance. Moreover, the use of glycolic acid as an activator for a magnesium chloride catalyst increased the fabric yellowing during the cure, even through the cure temperature needed was lowered by the glycolic acid.
A further reference pertinent to the present invention is that of Meyer et al, Textile Research Journal 46 691-697 (1976). Since alpha-hydroxy acids are known to be catalyst activators primarily with metal halide catalysts, a comparison of the use of tartaric acid with nine different metal halides was made to determine if improved strength retention during durable press finishing to a given level of wrinkle recovery angle could be obtained at the lower cure temperatures made possible by the presence of the tartaric acid. Meyer et al conclusively demonstrated that with formaldehyde as the nonnitrogenous durable press reagent, "a very small, barely significant improvement" in textile strength retention was obtained on lowering the cure temperature to 85.degree.-125.degree., as compared to 160.degree. C. used without the tartaric acid as catalyst activator. By contrast, the nitrogenous durable press reagent, dimethylolethyleneurea (DMEU), a widely used N-methylol agent, showed a very significant improvement in textile strength retention when cured at the lower temperatures with tartaric acid-metal halide catalyst as compared to high temperature curing without the tartaric acid as activator. In a second study, Meyer et al, Textile Research Journal 46 813-817 (1976) concluded that the poorer strength retention obtained with formaldehyde than with DMEU is due to greater acid-catalyzed degradation of cotton cellulose during the heat cure with formaldehyde, than occurs with DMEU as the durable press reagent. The strength retention was stated to increase, the higher the concentration of DMEU used, and the observation was made that DMEU buffers acid catalysts to partially supress cellulose degradation by the acid catalyst. These prior art results suggest that increased strength loss is inherent to the use of a non-nitrogenous cellulose crosslinking agent in acid-catalyzed durable-press finishing of fabrics high in cotton content.